---
title: "CVE-2021-27850: Bypass of the fix for CVE-2019-0195 | CubePath"
description: "A critical unauthenticated remote code execution vulnerability was found all recent versions of Apache Tapestry. The affected versions include 5.4.5…"
language: en
source: https://cubepath.com/security/cve/CVE-2021-27850
---

# CVE-2021-27850: Bypass of the fix for CVE-2019-0195 | CubePath

## Description

A critical unauthenticated remote code execution vulnerability was found all recent versions of Apache Tapestry. The affected versions include 5.4.5, 5.5.0, 5.6.2 and 5.7.0\. The vulnerability I have found is a bypass of the fix for CVE-2019-0195\. Recap: Before the fix of CVE-2019-0195 it was possible to download arbitrary class files from the classpath by providing a crafted asset file URL. An attacker was able to download the file \`AppModule.class\` by requesting the URL \`http://localhost:8080/assets/something/services/AppModule.class\` which contains a HMAC secret key. The fix for that bug was a blacklist filter that checks if the URL ends with \`.class\`, \`.properties\` or \`.xml\`. Bypass: Unfortunately, the blacklist solution can simply be bypassed by appending a \`/\` at the end of the URL: \`http://localhost:8080/assets/something/services/AppModule.class/\` The slash is stripped after the blacklist check and the file \`AppModule.class\` is loaded into the response. This class usually contains the HMAC secret key which is used to sign serialized Java objects. With the knowledge of that key an attacker can sign a Java gadget chain that leads to RCE (e.g. CommonsBeanUtils1 from ysoserial). Solution for this vulnerability: \* For Apache Tapestry 5.4.0 to 5.6.1, upgrade to 5.6.2 or later. \* For Apache Tapestry 5.7.0, upgrade to 5.7.1 or later.

Official description from the CVE record, published by apache. Copyright © 1999-2026 The MITRE Corporation. See [/security/cve/legal](https://cubepath.com/security/cve/legal) for the CVE license. [View the record on cve.org](https://www.cve.org/CVERecord?id=CVE-2021-27850)

## Key data

### EPSS

Exploit Prediction Scoring System by FIRST: an estimate of the probability that exploitation activity will be observed in the next 30 days.

Score

0.93560 (93.6% probability)

Percentile

99.8%

Scores of

Nov 10, 2026

Model

v2026.06.15

### Weakness (CWE)

CWE catalog version 5.0.

CWE names: Copyright © 2006-2026, The MITRE Corporation. See [/security/cve/legal](https://cubepath.com/security/cve/legal) for the CWE license.

- [CWE-200](https://cwe.mitre.org/data/definitions/200.html) Exposure of Sensitive Information to an Unauthorized Actor
- [CWE-502](https://cwe.mitre.org/data/definitions/502.html) Deserialization of Untrusted Data

## Affected products

Products listed in the CVE record, as the CNA published them.

- Apache Tapestry

  - affected: Apache Tapestry 5.5.0
  - affected: Apache Tapestry 5.7.0
  - affected: Apache Tapestry 5.4.5 up to before Apache Tapestry 5.4.0\*
  - affected: Apache Tapestry 5.6.2 up to before Apache Tapestry 5.6.0\*

## References

Links listed in the CVE record. They lead to other sites, which CubePath does not control.

- [lists.apache.org/thread.html/r237ff7f286bda31682c254550c1eb…](https://lists.apache.org/thread.html/r237ff7f286bda31682c254550c1ebf92b0ec61329b32fbeb2d1c8751%40%3Cusers.tapestry.apache.org%3E)
- [\[oss-security\] 20210414 CVE-2021-27850: Apache Tapestry: Bypass of the fix for CVE-2019-0195](http://www.openwall.com/lists/oss-security/2021/04/15/1)  (openwall.com) mailing-list
- [security.netapp.com/advisory/ntap-20210528-0002](https://security.netapp.com/advisory/ntap-20210528-0002/)

## Timeline

1. ID reserved Mar 1, 2021
2. Record published Apr 15, 2021
3. Record last updated Aug 3, 2024

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## About CubePath

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Data from the CVE Program (MITRE), CISA KEV and FIRST EPSS. CVSS is owned by FIRST and used by permission. Not affiliated with or endorsed by MITRE, CISA or FIRST. Data as of Nov 10, 2026, 20:05 UTC. [Sources and licenses](https://cubepath.com/security/cve/legal)